SD_JOURNAL_NEXT(3) sd_journal_next SD_JOURNAL_NEXT(3)NAME
sd_journal_next, sd_journal_previous, sd_journal_next_skip,
sd_journal_previous_skip, SD_JOURNAL_FOREACH,
SD_JOURNAL_FOREACH_BACKWARDS - Advance or set back the read pointer in
the journal
SYNOPSIS
#include <systemd/sd-journal.h>
int sd_journal_next(sd_journal* j);
int sd_journal_previous(sd_journal* j);
int sd_journal_next_skip(sd_journal* j, uint64_t skip);
int sd_journal_previous_skip(sd_journal* j, uint64_t skip);
SD_JOURNAL_FOREACH(sd_journal* j);
SD_JOURNAL_FOREACH_BACKWARDS(sd_journal* j);
DESCRIPTIONsd_journal_next() advances the read pointer into the journal by one
entry. The only argument taken is a journal context object as allocated
via sd_journal_open(3). After successful invocation the entry may be
read with functions such as sd_journal_get_data(3).
Similarly, sd_journal_previous() sets the read pointer back one entry.
sd_journal_next_skip() and sd_journal_previous_skip() advance/set back
the read pointer by multiple entries at once, as specified in the skip
parameter.
The journal is strictly ordered by reception time, and hence advancing
to the next entry guarantees that the entry then pointing to is later
in time than then previous one, or has the same timestamp.
Note that sd_journal_get_data(3) and related calls will fail unless
sd_journal_next() has been invoked at least once in order to position
the read pointer on a journal entry.
Note that the SD_JOURNAL_FOREACH() macro may be used as a wrapper
around sd_journal_seek_head(3) and sd_journal_next() in order to make
iterating through the journal easier. See below for an example.
Similarly, SD_JOURNAL_FOREACH_BACKWARDS() may be used for iterating the
journal in reverse order.
RETURN VALUE
The four calls return the number of entries advanced/set back on
success or a negative errno-style error code. When the end or beginning
of the journal is reached, a number smaller than requested is returned.
More specifically, if sd_journal_next() or sd_journal_previous() reach
the end/beginning of the journal they will return 0, instead of 1 when
they are successful. This should be considered an EOF marker.
NOTES
The sd_journal_next(), sd_journal_previous(), sd_journal_next_skip()
and sd_journal_previous_skip() interfaces are available as a shared
library, which can be compiled and linked to with the libsystemd pkg-
config(1) file.
EXAMPLES
Iterating through the journal:
#include <stdio.h>
#include <string.h>
#include <systemd/sd-journal.h>
int main(int argc, char *argv[]) {
int r;
sd_journal *j;
r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
if (r < 0) {
fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
return 1;
}
SD_JOURNAL_FOREACH(j) {
const char *d;
size_t l;
r = sd_journal_get_data(j, "MESSAGE", &d, &l);
if (r < 0) {
fprintf(stderr, "Failed to read message field: %s\n", strerror(-r));
continue;
}
printf("%.*s\n", (int) l, d);
}
sd_journal_close(j);
return 0;
}
SEE ALSOsystemd(1), sd-journal(3), sd_journal_open(3), sd_journal_get_data(3),
sd_journal_get_realtime_usec(3), sd_journal_get_cursor(3)systemd 212SD_JOURNAL_NEXT(3)
